Anything better than 10 guage Romex?

In the USA Belden 83803 is not approved for branch circuit power wiring per NEC (National Electrical Code).... As far as the manufacture specs, it is designed and UL approved for Power Limited Fire Alarm, (PLFA Class 3)wiring.

NEC 760.121 (A)(1), (A)(2), or (A)(3)

My only reason for pointing out the Belden cable is not approved for branch circuit power wiring is for the OP's and others benefit..... If the cable is used in a manner it is not intended as well as not Listed, approved, and for what ever reason there was a fire or personal injury an insurance claim could be denied by the insurance company.

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You might ask where in a fire alarm system would #12 wire be used? Horn, or Horn/Strobe circuits...

Can it, legally, be called a "power cord" or "extension" if it has the IEC connection on the end?

Not if it's in the wall and not removable.

The best option is metal conduit, because it's shielded and so less likely to radiate hum. BX is second best, for the same reason. Stranded vs. solid doesn't matter, except insofar as stranded is easier to manipulate in heavy gauges. Gauge does -- the thicker the wire, the less voltage drop. As someone pointed out, wiring heavy gauge wire to a standard receptacle can be tricky. Agree that you shouldn't use the Belden, which would violate code.

I see that Cardas sells a 10 guage in wall wire.

Now I have another one to decide.

The JPS is just a bit too expensive.

The wiring isn't inside the walls but is suspended off the floor and I only need two runs about 10 ft each.

One line from the 30 watt breaker at the panel,is wired to a Wattgate 20 amp receptacle and then into a Hydra 2 and that powers the amps.

The other 10 guage romex line is wired from another 30 amp breaker(on the same phase)and is wired to a potted Shunyata dual receptacle croyd receptacle and into it is a Hydra Annaconda 20 amp PC into a Hydra 8.

I am curious, after giving more information,what others feel about the best choice of wiring to be in this instance.

I wouldn't want the resolution of one brand of wire to be wiped out by the colourations of another.
Best case scenario would be wires from Shunyata I would presume.

Perhaps since they are into doing studios, they should delve into this area.
Seems like a natural to me for them.

How about some venom power cables unterminated?

The other line